Wankel machines are well known in the art, as were first described in U.S. Pat. No. 2,988,065 to Wankel.
Stirling machines are well known in the art, and operate on the basis of closed-loop compression and expansion of a compressible working fluid. The basic elements of a Stirling machine include an expander, a compressor, heat input, heat rejection, and regenerators. The regenerators act as a thermal capacitor to accept and reject heat from or to the working fluid as it transfers between the compressor and the expander, to increase efficiency.
U.S. Pat. No. 3,509,718 to Fezer et al. teaches a hot gas machine having first and second epitrochoidal housings, each containing rotatable triangular pistons having their interior divided into piston chambers, one housing/piston forming hot chambers and the other housing/piston forming cold chambers. The pistons rotatable on an eccentric shaft while being interconnected by double wall pipe means, the double wall pipe means allowing fluid communication between the hot chambers and the cold chambers. The double wall pipe means may also have regenerator means within an annular intermediate section.
Current designs in Wankel type machines involve inlet and outlet ports in the housing. These designs may result in significant counter-rotation force or shock pressure as the pressurized chambers pass over the inlet and outlet ports.
U.S. Pat. No. 6,109,040 to Ellison et al. teaches a stirling cycle refrigerator or engine employing a rotary wankel mechanism incorporating two Wankel rotary pistons, each in a housing only having two ports and interconnected by only two separate oscillating-flow, closed-cycle regenerative passages.